Hydraulic damping elements are used in many fields of technology in particular where a smooth and continuous rotary movement of a shaft is important; in heads of tripods for movie and television cameras therefor hydraulic damping elements are preferred in order to be able to follow a scene with the camera evenly and controlled and in order to achieve during a showing of the developed film an optically comfortable film image without so-called vibratory motions.
The damping elements which are considered here have two sets of damping elements interleafed comblike and having surface gaps therebetween filled with a damping fluid. The one set of damping elements is connected rigid against rotation to the shaft about which the rotary movement occurs, while the second set is yieldingly held and causes, during a rotary movement of the two sets relative to one another, the creation of shearing forces through adhesion in the surface gaps which are opposite the rotary movement to dampen and sudden acceleration forces.
Such hydraulic damping elements can therefore only be used in connection with heavy tripods which are bulky to transport, as they are used substantially only by professional movie makers in connection with heavy movie and television cameras. Movie amateurs, however, which usually use much lighter and more handy cameras, hesitate to buy them because of the mentioned difficulties in handling the heavy hydraulically damped tripods, even if they take a lot of movies and know of the advantages of these tripods.
As damping elements, annular disks (German OS No. 24 57 267 or U.S. Pat. No. 2,514,137) or annular cores (compare German Pat. No. 1 937 011) are used.
The known damping elements have each a separate housing which in most cases is composed of castings and is filled with a damping fluid, in which housing the shaft and the two sets of damping elements are arranged. The second set of damping elements is locked either entirely in the housing (compare U.S. Pat. No. 2,514,137) or, however, there exists the possibility to lock only individual damping elements selectively with the housing to cause different damping forces to be achievable; compare German OS No. 24 57 267 and German Patent No. 19 37 011.
The mentioned construction of a damping element with a housing which is composed of castings brings about that the entire damping element is heavy and bulky. In particular in the case of heads of tripods for movie and television cameras this has the consequence that also the tripod which carries the head must be designed accordingly massive in order to assure a clearance-free and blurfree swivelling of the camera.
In addition, the manufacture and the assembly of known damping elements, possibly in connection with heads of tripods, is complicated and expensive, even if partly it has been tried to use premanufactured parts with the same dimensions; thus according to German OS No. 24 57 267 the annular disks which serve as damping elements and the spacers, which assure the spacing between the annular disks, are punched of sheet metal. In spite of this simplification, the assembly of the damping element must, however, be generally done manually; thus a head of a tripod with adjustable damping force is for example successively built of the individual parts of the damping element and the housing and operations are needed which cannot be automated. Also the utilization of smaller tool machines, which serve only to support the manual operations, thus assembly and screwing together of the individual parts, is only possible in a limited scope.
Because of the high manufacturing expenses, such damping elements are naturally expensive. In the case of hydraulically damped heads of tripods, this leads to these being sold only in limited numbers and substantially again only to professional film makers, since the purchase is only economical for these professional circles. However, the price for such heads of tripods is in relationship to the intended use too high for movie amateurs.
The basic purpose of the invention is to newly design the construction of a hydraulic damping element and to substantially simplify same. Particularly the damping element is to be composed of parts which permit a simple and thus inexpensive manufacture and it is possible to also use more tool machines; furthermore the building size of the damping element is to be reduced.
Contrary to known damping elements, a damping element according to the invention is constructed as a separate closed unit, which can be manufactured independent from the device which must be connected to the damping element, for example a head of a tripod or a housing which receives it. Due to the fact that the damping element is first built as a structural unit without its own separate housing, the operating steps are cancelled which had been necessary up to now for the described successive assembly of the housing with the individual damping elements. The finished package-shaped damping element is now moved with its hub onto the shaft, is fixed with same and in this manner for example connected to the head of the tripod.
The damping element can be manufactured in an organized and inexpensive manner, particularly when the damping elements are annular disks. The first subunit is hereby composed alternately of annular disk-shaped spacers and annular disks with the same hole diameter, while the second subunit is composed alternately of annular disks and annular disk-shaped spacers which are connected to said annular disks and which have each the same outside diameter.
At least the two outer annular disks of the second subunit, which annular disks define the damping element, are supported on spacers of the first subunit and sealing means, for example 0-rings, are provided for sealing off the first subunit with respect to these outer annular disks of the second subunit. In the case of such a construction, thus the sealing disks and the annular disks of the first subunit form with their equal hold diameters the hub, while the annular disks of the second set are interleafed between the annular disks of the first subunit. At least the two outer annular disks of the second subunit slide on the corresponding spacers of the first subunit, thus have an inside diameter which corresponds to the outside diameter of the spacers. To seal off the damping element, preferably O-rings are arranged between outer annular disks and associated spacers.
One damping element according to the invention consists of a structural unit defined only by the annular disks which contribute to the damping and the spacers, and the two O-rings for sealing. It can be seen that with such a construction, a very compact structure is achieved, in which also very thin sheet metal can be used for the annular disks and spacers, without that the mechanical rigidity of the entire damping package would be lessened. In spite of a structural size which is substantially reduced compared with known damping elements, very high damping forces can be achieved.
An important advantage of such a damping elements lies in the possibility of substantially automating and speeding up the manufacture by using tool machines. Annular disks and spacers are first punched from sheet metal; then alternately spacers and annular disks of the first subunit and the corresponding parts of the second subunit are placed one on top of the other and are each coated with damping liquid. In the outer annular disks, the O-ring is inserted in addition. The thus formed package is compressed and the excessive damping liquid exits from the gaps between the spacers and annular disks; subsequently the annular disks and the spacers of the outer subunit which supports the second set of the annular disks are connected, for example by riveting; through this the entire package is held together. The first subunit, consisting of the suitable spacers and annular disks need in this case be connected only lightly, for example by pinning, to secure the individual parts against rotation.
The entire manufacture of the damping element requires only a fraction of the time heretofore used for manual assembly of a damping element in a housing; the manufacture of a head of a tripod with such a damping element is less expensive; if the heretofore assembly of the entire head took place successively of parts of the head of the tripod and the damping element, which caused a so-called intermeshed and interdependent manufacture of the head of the tripod and of the damping head, then now it is possible to assemble very simply a head of a tripod from the already finished damping element and the prepared housing of the head in a few operating steps.
The hub of the damping element preferably projects slightly beyond the second subunit which is supported on same, namely in a construction with annular disks the outer spacers of the first subunit project slightly beyond the two outer annular disks of the second subunit which define the damping element. As a result, the damping element which is constructed as a package fixed to the shaft by a press fit, so that the freedom of movement of the second subunit and therewith also the two outer annular disks are not affected. In addition, it is also possible to provide the hub of the damping element, namely the spacers and annular disks of the first subunit, with teeth which correspond with the shaft; thus a clearance-free fit which is necessary for a smooth damping of the rotary movement is assured.
According to an advantageous application of the invention, several such package-shaped damping elements can be moved on the shaft and can be connected rigid against rotation to same; through a locking mechanism, as it can be taken over in principle approximately from German OS No. 24 57 267, the damping elements can be selectively held on their periphery, namely the respectively second subunits of the individual damping elements, so that in a very simple manner it is possible to vary the damping factor. Such a damping element with a selectable adjustment of the damping factor is structurally much simpler than known damping elements, because the entire locking mechanism is arranged outside of the damping elements because of the package-shaped closed structure of the individual damping elements.
In known damping elements, care had to be taken, either through particularly precise manufacture or through separate sealing means, to assure that the operating levers for locking the individual damping elements are guided leakage-free from the housing; these problems do not at all occur in an adjustable damping element according to the invention.
Also damping elements with a variable damping factor can be manufactured simply and with many possibilities of adjustment. Thus it is possible to achieve eight progressive damping stages approximately through three package-shaped damping elements, the number of which can be selectively adjusted correspondingly to one another to assure that the manufacture expense for the entire unit is not substantially increased. Since in the package-shaped damping elements according to the invention, the damping elements can be punched from very thin sheet metal, a compact device having a high damping factor can be achieved.
Since damping elements can be manufactured with the given construction at a small and favorable price, it is here also possible to manufacture hydraulically damped heads of tripods substantially less expensively and to couple same with light and handy tripods, as they are used by movie amateurs.